This is a question that was brought to us by a longtime Wavefront user, and it's definitely possible! Let's start with the final query and then I'll explain how it works.
(timestamp(ts(cpu.loadavg.1m, tag=dev*)) - last(timestamp(ts(cpu.loadavg.1m, tag=dev*))))
The query above shows the time that's passing in between reported values. It continues to climb in value until the next value is reported, and then starts the count all over. The first portion of the query, timestamp(ts(cpu.loadavg.1m, tag=dev*)), returns the epoch time for any value being reported for cpu.loadavg.1m. The second portion of the query does the same thing, but returns the epoch time for the last known reported value. Then we simply subtract the second argument from the first argument in order to determine how much time passed between reported values.